De ruiende Bergeenden Tadorna tadorna in het Haringvliet

During the years 1976-1987 observations were made on a concentration moulting Shelduck on the Haringvliet in the province of Zuid-Holland in the Netherlands. After the closure in 1970 the Haringvliet became a freshwater area with a tidal difference of about 40 centimeters. The moulting Shelducks gather on the Ventjagersplaten, situated about 50 kilometers inland. The area consists of an isolated bank with wide shallowing waters around, called the Ventjagersgaatje. The southern side of the area is bounded by tidal mudflats. As a part of the Deltaworks these mudflats were liquidated spring 1987. The Ventjagersplaten have also an important function as a summer -concentration-place for Shelduck (Ouweneel 1976). Table 1 shows how the majority of the Shelduck leave the area In the middle of July. The birds which spend their wingmoult on the Ventjagersplaten concentrate in big flocks in the middle of the Ventjagersgaatje. The first moulting Shelduck were observed on the 10th of July, the latest on the 2nd of September. Table 2 shows the maximum number of moulting Shelduck, observed on one day annually. Generally around the middle of august the moulting -concentration is reaching its highest peak. Because of the birds do not moult on the same time the real number of moulting Shelduck annually, will lay some hundreds higher than the numbers showed on table 2. The author does not know other Shelduck-moulting areas on freshwater.